Conventional water heaters provide heated water by storing heat energy in the water. Because the heat energy is stored in the water, a large portion of the heater must be dedicated to storing the heated water until it is used. Typically, water stores approximately 10 calories/gram of heat per 10.degree. C. increments. By requiring a large portion of the heater for storage of heated water, the water heater must be of reasonable size to store enough heated water for use in a standard residential environment. Typical residential water heaters have a 30-40 gallon capacity. For use in buildings and industry, water heaters must be even larger.
Water heaters consume a high percentage of residential energy heating water for bathing, washing dishes, washing clothes and heating homes and offices. In homes heated by electricity, the consumption of electric power is even greater. Overall, a large imbalance in electric power usage exists during the day time due primarily to the large amounts of power consumed by industry, businesses and public transportation. In many locations, day time peak usage is twice that of the night hours. To compensate for the extensive day time use of electric power, utility companies provide generating capacity sufficient to supply day time usage, leaving unused capacity available for the night hours.
In order to reduce an ever expanding need for day time power, utility companies are providing incentive pricing for off-peak power usage to encourage more use of the existing surplus night power capacity. This practice is common in Japan, in some European countries, and in a few locations in the United States.
Further, the ever increasing use of fossil fuels world wide for heating and cooling applications contributes significantly to the depletion of irreplaceable raw materials. Additionally, the burning of fossil fuels of all kinds is resulting in atmospheric pollution with nitrogen oxides and in higher concentrations of carbon dioxide in the atmosphere. The carbon dioxide buildup is of increasing concern because it may eventually result in drastic changes in global climates through global warming.
Thus, a need has arisen in the art for a water heater which can more efficiently heat water, which can make effective use of utilities during off-peak hours to minimize building and household power consumption and which would consequently reduce building and household utility costs. Further, there is an urgent need to adopt energy conservation technologies to stretch the supply of available fossil fuels until non-polluting energy can be developed and implemented.